In marine, brackish, and freshwater environments, organisms collect, settle, attach, and grow on submerged structures. Organisms which do so can include algae, fungi, microbes, and aquatic animals, such as tunicates, hydroids, bivalves, bryozoans, polychaete worms, sponges, and barnacles. Submerged structures can include the underwater surfaces of ships, docks and piers, pilings, heat exchangers, dams, piping structures, such as intake screens, and cooling towers. The presence of these organisms, known as the "fouling" of a structure, can be harmful in many respects. They can add to the weight of the structure, hamper its hydrodynamics, reduce its operating efficiency, increase susceptibility to corrosion, and degrade or even fracture the structure.
The common method of controlling the attachment of fouling organisms is by protecting the structure to be protected with a paint or coating which contains an antifouling agent. Exemplary antifouling coatings and paints are described in U.S. Pat. No. 4,596,724 to Lane, U.S. Pat. No. 4,410,642 to Layton, and U.S. Pat. No. 4,788,302 to Costlow. Application of a coating of this type inhibits the attachment, or "settling", of the organism, by either disabling the organism or providing it with an unattractive environment upon which to settle.
Of the fouling organisms noted above, barnacles have proven to be among the most difficult to control. Typically, commercial antifouling coatings and paints include a toxic metal-containing compound such as tri-n-butyl tin (TBT), or cuprous oxide, which leaches from the coating. Although these compounds exhibit moderate success in inhibiting barnacle settlement, they degrade slowly in marine environments, and therefore are ecologically harmful. In fact, TBT is sufficiently toxic that its release rate is limited by legislation in some countries.
Some experimental non-toxic compounds have been tested with limited success in barnacle settlement inhibition. See, e.g., Gerhart et al., J. Chem. Ecol. 14:1905-1917 (1988), which discloses the use of pukalide, epoxypukalide, and an extract produced by the octocoral Leptogorgia virgulata, to inhibit barnacle settlement; Sears et al., J. Chem. Ecol. 16:791-799 (1990), which discloses the use of ethyl acetate extracts of the sponge Lissodendoryx isodictyalis to inhibit settlement; and Japanese Patent Disclosure No. 54-44018A of Apr. 7, 1979, which discloses the use of gamma-methylenebutenolide lactone and alkyl gamma-methylenebutenolide lactone derivatives.
In view of the foregoing, it is a first object of the present invention to provide a non-toxic antifouling compound which effectively inhibits the settlement of barnacles on an underwater surface.
It is a second object of the present invention to provide an antifouling paint or coating which releases the aforementioned antifouling compound.